In a networked environment, email may be routed from a sending client over the network to one or more destination recipient mailbox servers. Conventional email routing sometimes involves routing an email message through proxy transport servers using simple mail transfer protocol (SMTP). The proxy transport servers may perform connection filtering, email message filtering (e.g., scanning for spam and viruses), and load balancing on the email message before transmission to the next processing server. The proxy transport servers perform these actions while maintaining the open connection from the sender, which may partly contribute to the time limitation.
Typically, when routing email through proxy transport servers, an external mail transfer agent may transmit the email message to a proxy transport server, and there is a limited amount of time available for selecting a working target server and transmitting the email message to the target server before the external mail transfer agent times out its connection. This may result in a limited number of working target servers being selected, and often times the selected working target servers may be located far away from a destination mailbox server resulting in inefficient email transmission, and also may result in unreliable transport servers which may be vulnerable to network outages.